1992 Mercedes Benz 190e parking break not holding car...fail

i have a mercedes 190e and i recently got my car inspected and it failed. originally the problem was the regular breaks themselves, but now its just the parking break. they told me the parking break does not hold the car. so i need to know, is there a way to adjust the parking break on this car? if so where do i do it? i have limited of time before i need to get the car inspected by the deadline. so if someone could help me, id deeply appreciate it. thanks
-Rob.